Anybody have any experiance with a Portec grinder ?

I am looking to purchase a grinder, my goal with this machine is to grind some trees and brush etc, also would like to be able to use it on larger structure demo sites just to "size" the material to minimize trucking cost. the questions I have are..... 1. Does anybody have any experiance with the tumble grinders or more particularly the Portec's ? 2. What are the drawbacks/advantages of a tumble grinder apposed to a tub grinder ? 3. Do you think it will work for my application ? thanks pj,